Half a croissant, on a plate, with a sign in front of it saying '50c'
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Heat/AC combo

Multi Mode Heat Pump
  [vote for,

This is an air cooler and heater, and which can also generate a small amount of mechanical energy (one or two extra horsepower, perhaps) when the passengers don't need heating or cooling.

It would have three heat exchangers: one in-cabin, air/refrigerant heat exchanger, one outside air/refrigerant heat exchanger, and one refrigerant/engine coolant heat exchanger. There would also be valves to select from various paths refrigerant could flow through the system.

The refrigerant compressor would need to be able to run in reverse, as an expander, and instead of having an expansion valve, it would have a reversible hydraulic motor/pump.

(1) When used for cooling, it would operate much like a conventional air conditioner, with refrigerant going from the compressor, to the external air cooled heat exchanger (here used as a condensor), to the hydraulic motor (here used instead of an expansion valve), to the inside heat exchanger (here used as an evaporator) and back to the compressor. This, of course, is a reverse Rankine cycle.

(2) However, if the cabin is already cool (and the engine is hot), it would operate in a different manner: liquid refrigerant would go from the hydraulic motor (here used as a pump), to the refrigerant/coolant heat exchanger, then through the gas compressor (used in reverse, as a gas expander), then through the outside air cooled heat exchanger. In this mode, it acts as a forward Rankine cycle heat engine, giving the engine extra power.

(3) When used for heating (when the engine is cold), refrigerant would go from the compressor, to the cabin air heat exchanger, to the hydraulic motor, to the outside air heat exchanger, to the coolant/refrigerant heat exchanger, then back to the compressor. In this mode, it acts much like it does in summer, using a reverse Rankine cycle, but moving heat from outside to inside the car.

(4) When used for heating (when the engine is hot), the cycle would be: hydraulic motor/pump (used as a pump), refrigerant/coolant heat exchanger, compressor/expander (used as an expander), cabin air heat exchanger, outside air heat exchanger, and back to the liquid pump. This cycle would generate mechanical power using a forward Rankine cycle. (If the engine is merely warm, not hot, then more inside warmth can be gotten by not sending the refrigerant through the outside heat exchanger)

And, of course, if the engine is hot, and the outside air is cold, and there's no desire for more heat in the cabin, we do the same thing as we did in summer, when the engine was hot and the cabin was cool enough: use the system as a forward rankine cycle, not involving the cabin air heat exchanger (mode 2).

goldbb, Feb 02 2009

or you could do this... Automobile_20pre-start_20system
[FlyingToaster, Feb 05 2009]


       A couple of things.   

       1. You can usually assume that there is always excess heat available from the engine for cabin heating - therefore you can achieve this in the conventional manner without the added complexity of a heat pump.   

       2. You can usually assume that there is adequate means of regulating engine temperature for optimum running (the existing radiator system) without the need for a heat pump there.   

       Other than the potential delivery of warm air to the cabin immediately after cold start-up, what is to gain from the added complexity of your system?
Texticle, Feb 02 2009

       Firstly, in cold climates, people often run their cars for tens of minutes to warm them up, wasting lots of fuel. Providing instant heat isn't just for comfort: By avoiding the need to warm the engine, it saves fuel and reduces pollution.   

       Secondly, running the system as a heat engine (when the engine is hot and there isn't demand for cabin cooling) isn't to "regulate engine temperature," but to generate a couple of extra horsepower from otherwise wasted heat.   

       The fact that it cools the engine coolant is an added bonus (which I didn't think of until you mentioned it), since that means that the coolant pump could possibly be run at a lower speed, thus consuming less of the engine's power output.
goldbb, Feb 03 2009

       goldbb did you happen to read my recent idea?
evilpenguin, Feb 04 2009

       UB, kinda redundant. I like to think I inspired this idea, just wasn't sure if I did.
evilpenguin, Feb 04 2009

       evilpenguin, I didn't read your post before writing mine.   

       They have little in common, besides that they're both ways to heat the cabin before the engine is hot.   

       (1) Although my device would replace parts of the ac system and parts of the heating system, it wouldn't need to be swapped out seasonly. It can switch between heating, cooling, and generating power merely by opening and closing valves. And this can easily be done automatically using thermostats.   

       (2) Your idea is to use electricity to generate heat, whereas mine is to use a heat pump.   

       Electricity produces heat at a mere 100% efficiency, whereas an air-source heat pump produces heat at about 150% to 300% efficiency.   

       (3) When the engine becomes hot enough to warm the cabin, your gadget merely turns off, whereas mine starts generating mechanical power. (except of course in summer, in which case my gadget only produces mechanical power when the thermostat indicates that the cabin is as cool as the pasengers want it to be)   

       (4) If my gadget were hooked up to either an electric or pneumatic car, it will drain much less mechanical energy from the engine to provide cabin heat than yours would, plus it could still provide cooling.
goldbb, Feb 05 2009

       Oh, and the "got here first" award goes to two people/groups.   

       BMW, who has supposedly build a car with an AC that can work as a heat pump to warm the cabin when the engine's cold.   

       Someone I read about a few months back, who retrofitted the car's AC system to work as a heat engine, using waste heat to produce mechanical power. They didn't make it so that it could still function as an AC or heater, though.
goldbb, Feb 05 2009


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